When discussing 19th-century astronomers, Edwin Hubble often comes to mind first. Known for discovering evidence of the expanding universe, he is celebrated as the 'Father of Extragalactic Astronomy'.

To commemorate his outstanding contributions to human astronomy, people even named a telescope of great importance to humanity after him—the Hubble Space Telescope.

However, there was not only one astronomer in the 19th century who made remarkable contributions to astronomy. There was another German astronomer named Olbers, who was well-known for explaining the formation principle of comet tails.

In today's era of advanced technology, we know that comets drag a "long tail" because when they enter the inner orbits of the solar system, they are affected by the light and heat emitted by the Sun, causing many of their originally solid substances to become gaseous and liquid, thus forming the "tail" we see.

But for people in the relatively technologically backward 19th century, comets were very mysterious celestial bodies. Therefore, after Olbers proposed the formation principle of comet tails, the mysterious color of comet tails began to gradually fade in people's minds, and he thus became a famous astronomer at that time.

Yet, Olbers is best known not for his work on comet tails but for posing a question in 1823 that remains unresolved today, known as 'Olbers' Paradox.

Olbers believed that since the universe is an infinite space filled with countless celestial bodies, then looking in any direction from Earth at the night sky should result in brightness, and there should be no dark patches as we observe now.

In essence, the true appearance of our night sky would be completely covered by countless celestial bodies distributed densely without any gaps (because there are so many of them), and the light emitted or reflected by these bodies would inevitably reach the Earth. Because the sky is filled with celestial bodies, the light from these bodies reaching Earth would converge, thus illuminating the entire night sky.

Therefore, theoretically, our night sky should be as bright as daylight. But why do we see the night sky as pitch black? This is the "Olbers' Paradox".

When the theory of cosmic expansion was proposed, and Edwin Hubble discovered conclusive evidence of the redshift of light, some people once believed that this theory could perfectly explain "Olbers' Paradox".

Because the universe is expanding, and the rate of expansion is much greater than the speed of light, this leads to many lights that cannot reach Earth, which we cannot see. Hence, this explains why the night sky is not as bright as daylight, but instead appears largely dark.

However, because the theory of cosmic expansion itself has many inconsistencies, most scientists do not agree with this explanation. This leads to the fact that even today, scientists are constantly building new models of the universe, attempting to unravel "Olbers' Paradox".

Although to this day "Olbers' Paradox" still lacks a universally accepted answer, it at least tells us a fact, and this fact can answer the question: Is the starry sky we see with our eyes the true appearance of the sky?

The answer is no. According to "Olbers' Paradox", our sky, whether it is day or night, is filled with countless celestial bodies, and there are no "gaps" between these bodies. This is the true appearance of our sky. The myriad stars we see in the night sky are only a very small fraction of these celestial bodies that fill the sky.

The term "very small fraction" cannot describe the defect of the human eye. According to authoritative statistics, about 95% of the stars visible at night are within 1,100 light-years of Earth, and about 75% are within 500 light-years of Earth.

Considering that the diameter of the entire Milky Way is about 200,000 light-years, if we compare 1,100 light-years to 200,000 light-years, the scale of this 1,100 light-years is like a sesame seed on a big pancake.

The shimmering stars in the night sky often give people the illusion that they have seen the infinitely distant horizon of the universe. The so-called "cosmic horizon" is only a tiny distance from the Milky Way, but it may be a distance that humanity may never be able to conquer, which can be somewhat despairing.

Most of the celestial bodies visible to the human eye in the night sky are stars that are larger and brighter than our sun, which is the fundamental reason why they can be seen even though they are far away from us.

In conclusion, Olbers' Paradox challenges our perception of the night sky, reminding us that what we see with our eyes is just a fraction of the vast cosmos. While the paradox remains unresolved, it prompts us to contemplate the true nature of the universe and our place within it. As we continue to explore and unravel its mysteries, the stars above serve as a timeless reminder of the boundless wonders that await discovery.